Formation treating for purposes of sand consolidation, water exclusion or well plugging for abandonment are well known terms applying to procedures routinely practiced in the commercial production of petroleum. When wells are completed in petroleum-containing formations which also contain unconsolidated granular mineral material such as sand or gravel, production of fluids from the formation causes the flow of the particulate matter, e.g. sand, into the wellbore, which often leads to any of several difficult and expensive problems. Sometimes a well will "sand up", meaning the lower portion of the production well becomes filled with sand, after which further production of fluid from the formation becomes difficult or impossible. In other instances, sand production along with the fluid results in passage of granular mineral material into the pump and associated hardware of the producing well, which causes accelerated wear of the mechanical components of the producing oil well. Sustained production of sand sometimes forms a cavity in the formation which collapses and destroys the well. All of these problems are known to exist and many methods have been disclosed in the prior art and applied in oil fields in order to reduce or eliminate production of unconsolidated sand from a petroleum formation during the course of oil production.
Another problem encountered in oil production to which the present process offers an attractive solution is encountered when a well is in fluid communication with a section that includes one or more oil producing intervals and one or more water-producing intervals. Production from such a zone results in production of some oil and some water. Since the viscosity of water is less than the viscosity of oil, a much larger volume of water than oil is frequently produced. Certain embodiments of the present invention allow creation of a fluid-impermeable barrier around the well in the water-producing intervals to reduce or eliminate the flow of water from the formation into the well.
In yet another embodiment, the resin-catalyst mixture can be used to completely plug a well which is to be abandoned. This embodiment requires a slightly greater volume of resin-catalyst mixture to be used, since the best results for this embodiment require that the interior of the well casing and/or tubing be filled completely with the resin for all or a substantial amount of its length. The long term durability of the material used to plug wells for abandonment is of high current interest because of the danger that salt water or petroleum might enter and contaminate fresh water-containing intervals.
The above-described sand control problems and potential solutions to the problems have been the subject of extensive research by the petroleum industry in the hope of developing techniques which minimize or eliminate the problems such as the production of sand particles into the producing well and associated equipment during the course of producing fluids from the formation. One general approach suggested in the prior art for consolidating sand to form a fluid permeable zone around the well involves consolidating the porous but unconsolidated sand structure around the wellbore in order to cement the loose sand grains together, thereby forming a permeable mass which will allow production of fluids from the formation into the well but which will restrain the movement of sand particles into the wellbore when used for fluid exclusion. Another approach involves removing a portion of the formation around the well and packing specially prepared granular material into the formation around the wellbore which is subsequently caused to be cemented together in a manner which maintains fluid permeability.
It is a primary objective of any successful sand consolidation method that a barrier be formed around the wellbore which restrains the movement of sand particles into the well while offering little or no restriction to the flow of fluids, particularly oil, from the formation into the wellbore where it can be pumped to the surface of the earth. Consolidation only needs to extend into the formation to a depth of 6 to 12 inches around the periphery of the perforations or other openings in the outer casing of the production well.
The objective of a water exclusion or fluid entry control process is to form an impermeable barrier around the well to prevent the flow of sand and formation fluids into the well. A process similar to that used to control sand problems can be used for plugging formation for water exclusion, provided the process is modified to cause creation of an impermeable barrier rather than a permeable barrier.
The objective of a well plugging process is similar to the water exclusion method described above, except that the interior of the well is also filled with the resin, to ensure that no fluid movement from one formation zone to another will occur after the well is abandoned.
A very important quality of a satisfactory sand consolidation method, plugging or water exclusion method is durability of the permeable or impermeable barrier formed around the wellbore. Once a permeable barrier is formed and the well is placed on production, there will be a continuing flow of fluids through the flow channels within the permeable barrier, and it is important that the barrier last for a significant period of time, e.g. several months and preferably years, without excessive abrasive wear or other deterioration of the consolidation matrix which would cause the particulate matter to flow once again into the wellbore.
It is also important that the material injected into the formation for all of my formation treating methods described above should be essentially unreactive during the period it is inside the wellbore, i.e. while it is being pumped down the well and positioned where it is desired adjacent to the perforations of the production casing. It is this desire to delay the polymerization reaction that has lead prior art methods to employ multi-step procedures in which first a catalyst is injected into the formation, after which the polymerizable resin-containing fluid is injected. While this reduces the propensity for the fluid to polymerize in the wellbore, it does give rise to several problems which constitute inherent weaknesses in many prior art methods for accomplishing sand consolidation. First, each separate injection step increases the time and cost associated with the well treatment by which sand consolidation, water shut off or well plugging is accomplished. Second, injection of catalyst into the formation in advance of the polymerizable fluid does not accomplish uniform mixing of catalyst with all of the polymerizable fluid which is needed to ensure optimum polymerization of the resin, which is essential for strength and durability of the consolidated mass. Use of aqueous fluids to inject catalyst often gives rise to the need for yet additional steps to clean the sand to remove formation petroleum so the catalyst will be absorbed by the sand and later mix with the subsequently injected resin containing fluid.